1. Field of the Invention
The present invention relates to a plane position detecting method of detecting a position or an inclination (plane position) of a substrate surface relative to an optical axis direction of a projection optical system, and an exposing method and an exposure apparatus using the same.
2. Description of the Related Art
Improvements in productivity are now strongly demanded as the current performance that is required in a semiconductor manufacturing apparatus, particularly in a sequential travel type semiconductor exposing apparatus known as a stepper. That is, a chip maker has to reduce the unit chip cost so as to be able to prevent a memory cost meeting chip replacement, to cope with the increase in the degree of integration along with the memory trend.
Under these circumstances, an exposure apparatus maker must provide an apparatus that can contribute to the improvement in productivity, in addition to providing a high performance, with basic properties such as resolution and positioning accuracy, and furthermore, must increase the processing capacity per unit time, i.e., the number of processed wafers.
Methods of reducing the stepping time of a semiconductor exposure apparatus used in a production site include methods proposed in Japanese Patent Publication No. 4-50731 and Japanese Patent Laid-Open No. 4-116414. These patent publications disclose methods of detecting a position or an inclination of a substrate surface during step travel on an XY plane of a substrate, such as a semiconductor wafer. With these methods, as compared to a conventional method of detecting a position of a substrate relative to a z-axis direction or an inclination of the XY plane through confirmation of positioning of the substrate at an exposing position on the XY plane, the timing of starting of the plane position correction (i.e., the correction of a position in the z-axis direction or an inclination in the XY plane) becomes earlier, thus making it possible to reduce the stepping time as a whole.
There are also proposed a method of reducing the stepping time by previously calculating a focus offset so that a measured value at a measuring position during step travel of a substrate (hereinafter, referred to as a "measuring position during travel") becomes equivalent to a measured value at an exposing position of the substrate, and positively utilizing a measured value of the plane position during travel, and a method of reducing the stepping time through reduction of the measuring time by performing measurement with a focus detection range limited by taking into account a continuous step travel.
To date, an exposure wavelength for an exposure apparatus in the process design for the manufacture of semiconductors has been selected corresponding to the wiring rule: for example, an i-line stepper is used for a 0.35-.mu.m rule, and a KrF excimer laser stepper for a 0.25-.mu.m rule. That is, the manufacturing has been performed with the exposure wavelength in use setting the limit of the resolution line width, and the limit for the focal depth has inevitably been set to a value of about 1.0 .mu.m, which has been shared by the equipment and the process.
However, a new policy has recently been adopted, to continue to use a KrF excimer laser in an exposure apparatus as the light source to serve as the exposure technique with the next generation, having a 0.18-.mu.m rule. There is also a move to utilize KrF excimer laser exposure until mass production of 1-giga DRAMs of 0.1-.mu.m rule is achieved. The development of refining techniques such as a phase shift mask and super-resolution, as well as improvement of intra-chip flatness resulting from the adoption of CMP (chemical-mechanical polishing) make important contributions to this general trend. The use of CMP is reported to permit the reduction of a chip stage in a trench structure to within about 50 nm, and it is now possible to design a high numerical aperture (high-NA) lens having a sharply reduced focal depth and to impart a resolution under that of the wavelength of the exposure light being used.
To cope with the decrease in the focal depth resulting from the tendency toward a high NA, on the other hand, it is necessary to further improve the correction accuracy of the focusing and leveling. More specifically, methods for assuring the accuracy of the chip stage on the process side are diverse among the various semiconductor chip makers, including CMP, PSM (phase shift mask) and RA (recessed array). The manufacture of chips of the same generation with different margins of focal depth for the individual semiconductor chip makers is about to begin. As a result, it may be necessary to achieve a higher correction accuracy for a particular process for individual semiconductor chip makers, particularly for a process in which it is difficult to achieve perfect frames by the application of the stacking method.
Under these circumstances, the present inventors have found that, in the conventional method of performing corrective driving by offset-correcting a measured value during travel, the offset reproducibility slightly varies with the position of a shot on a wafer serving as the substrate, so that the correction accuracy may, in some cases, deviate from the standard, depending upon the position of the shot on the wafer.
This is chiefly attributable to the fact that, because the exterior shape of the wafer itself has been scaled up in order to cope with a 300-mm wafer and the like, and the amplitude (Z-direction) of the structural deformation in the tilting direction of the stage becomes larger along with the expansion of the wafer in the radial direction, a difference occurs in reproducibility of any offset between the wafer periphery and inside portions of the wafer. This instability, which is within a tolerable range in the conventional accuracy, leads to a non-negligible amount when covering a residual chip stage, as mentioned above, on the exposure apparatus side.
In a conventional method of focusing by limiting the focus detection range to reduce the stepping travel time, in a sequence other than exposure, such as during the execution of a step command after execution of a user operation, the surface to be detected may sometimes exceed the focus detection range, which may cause stoppage of the sequence.